In certain types of specific mixtures, it is known to make compatible two incompatible polymers by associating them with a third polymer, eventually sequenced or grafted, which is partially compatible with one and the other of the polymers. That is, for example, the case of the polyethylene-polystyrene mixture made compatible by a hydrogenated styrene-butadiene sequenced polymer.
The disadvantages of this method is that it does not disclose products that allow making systematically compatible two incompatible polymers. For example, it is now always known to make compatible couples, such as, polyamides-polyfluorinated, polyethylene-polyfluorinated, polyether block amide-poly(vinylchloride), styrenic resins-polyfluorinated. For associating such couples, it could be devised to incorporate into them as a mixture a third polymer in a quantity such that it could not be possible to speak of a compatibility agent but of a real three-compound mixture.
For those skilled in the art the compatibility agent serves only to modify the interfacial properties in two phases constituted by the two polymers to be made compatible without in itself constituting a third phase. It is for this reason that the effective compatibility agents are used only in small doses in the mixture of polymers to be made compatible, generally in a quantity below about 5% by weight of the mixture.